Java expert help me. A NullPointerException !!! I can't solve it.

Question

I have complied 3 files (SerialBean.java;SerialBuffer.java;ReaderSerial.java) as my package successfully, it is named serial. The package extends javax.comm.*; I wanna do some serial work.
Then I maked an application :SerialExample1
--------------------------------------code----------------------------------
----------------------------SerialExmaple1.java-----------------------------
import serial.*;
import java.io.*;
import javax.comm.*;
public class SerialExample1
public static void main(String args[])
SerialBean sB=new SerialBean(1);
sB.Initialize();
sB.WritePort("Hi,Chrono");
sB.ClosePort();
It is good enough to deliver the String "Hi,Chrono".
Then I maked another windows application :SerialExample2
------------------------------------code-------------------------------------
-----------------------------Frame1.java-------------------------------------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import com.borland.jbcl.layout.*;
import serial.*;
import java.io.*;
import javax.comm.*;
public class Frame1 extends JFrame
private JPanel contentPane;
private XYLayout xYLayout1 = new XYLayout();
private Button button1 = new Button();
private TextField textField1 = new TextField();
private SerialBean sB=new SerialBean(1);
//Construct the frame
public Frame1()
enableEvents(AWTEvent.WINDOW_EVENT_MASK);
try
jbInit();
catch(Exception e)
e.printStackTrace();
//Component initialization
private void jbInit() throws Exception
//setIconImage(Toolkit.getDefaultToolkit().createImage(Frame1.class.getResource("[Your Icon]")));
contentPane = (JPanel) this.getContentPane();
button1.setLabel("button1");
button1.addActionListener(new Frame1_button1_actionAdapter(this));
contentPane.setLayout(xYLayout1);
this.setSize(new Dimension(400, 300));
this.setTitle("Frame Title");
textField1.setText("textField1");
contentPane.add(button1, new XYConstraints(54, 52, -1, -1));
contentPane.add(textField1, new XYConstraints(195, 57, -1, -1));
//Overridden so we can exit when window is closed
protected void processWindowEvent(WindowEvent e)
super.processWindowEvent(e);
if (e.getID() == WindowEvent.WINDOW_CLOSING)
System.exit(0);
void button1_actionPerformed(ActionEvent e)
sB.Initialize();
sB.WritePort("Hi Chrono");
sB.ClosePort();
class Frame1_button1_actionAdapter implements java.awt.event.ActionListener
private Frame1 adaptee;
Frame1_button1_actionAdapter(Frame1 adaptee)
this.adaptee = adaptee;
public void actionPerformed(ActionEvent e)
adaptee.button1_actionPerformed(e);
---------------------------SerialExample2.java--------------------------------
import javax.swing.UIManager;
import java.awt.*;
public class SerialExample2
private boolean packFrame = false;
//Construct the application
public SerialExample2()
Frame1 frame = new Frame1();
//Validate frames that have preset sizes
//Pack frames that have useful preferred size info, e.g. from their layout
if (packFrame)
frame.pack();
else
frame.validate();
//Center the window
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Dimension frameSize = frame.getSize();
if (frameSize.height > screenSize.height)
frameSize.height = screenSize.height;
if (frameSize.width > screenSize.width)
frameSize.width = screenSize.width;
frame.setLocation((screenSize.width - frameSize.width) / 2, (screenSize.height - frameSize.height) / 2);
frame.setVisible(true);
//Main method
public static void main(String[] args)
try
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
catch(Exception e)
e.printStackTrace();
new SerialExample2();
It is a bad code!!! I compiled them seccessfully but It can't work .The java system gave
some wrong messages
Exception occurred during event dispatching:java.lang.NullPointerException     at serial.SerialBean.WritePort(SerialBean.java:115)     at Frame1.button1_actionPerformed(Frame1.java:66)     at Frame1_button1_actionAdapter.actionPerformed(Frame1.java:82)     at java.awt.Button.processActionEvent(Button.java:329)     at java.awt.Button.processEvent(Button.java:302)     at java.awt.Component.dispatchEventImpl(Component.java:2593)     at java.awt.Component.dispatchEvent(Component.java:2497)     at java.awt.EventQueue.dispatchEvent(EventQueue.java:339)     at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:131)     at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:98)     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)     at java.awt.EventDispatchThread.run(EventDispatchThread.java:85)-----------------------------------------------------------------------------------
I tried to debug it in Frame1.java:66 and SerialBean.java:115 but I can not find any error.
How to deal with it?
Here are the code about package serial
-----------------------------------code--------------------------------------------
----------------------------SerialBean.java----------------------------------------
package serial;
import java.io.*;
import java.util.*;
import javax.comm.*;
* This bean provides some basic functions to implement full dulplex
* information exchange through the srial port.
public class SerialBean
static String PortName;
CommPortIdentifier portId;
SerialPort serialPort;
static OutputStream out;
static InputStream in;
SerialBuffer SB;
ReadSerial RT;
* Constructor
* @param PortID the ID of the serial to be used. 1 for COM1,
* 2 for COM2, etc.
public SerialBean(int PortID)
PortName = "COM" + PortID;
* This function initialize the serial port for communication. It startss a
* thread which consistently monitors the serial port. Any signal capturred
* from the serial port is stored into a buffer area.
public int Initialize()
int InitSuccess = 1;
int InitFail = -1;
try
portId = CommPortIdentifier.getPortIdentifier(PortName);
try
serialPort = (SerialPort)
portId.open("Serial_Communication", 2000);
} catch (PortInUseException e)
return InitFail;
//Use InputStream in to read from the serial port, and OutputStream
//out to write to the serial port.
try
in = serialPort.getInputStream();
out = serialPort.getOutputStream();
} catch (IOException e)
return InitFail;
//Initialize the communication parameters to 9600, 8, 1, none.
try
serialPort.setSerialPortParams(9600,
SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
} catch (UnsupportedCommOperationException e)
return InitFail;
} catch (NoSuchPortException e)
return InitFail;
// when successfully open the serial port, create a new serial buffer,
// then create a thread that consistently accepts incoming signals from
// the serial port. Incoming signals are stored in the serial buffer.
SB = new SerialBuffer();
RT = new ReadSerial(SB, in);
RT.start();
// return success information
return InitSuccess;
* This function returns a string with a certain length from the incomin
* messages.
* @param Length The length of the string to be returned.
public String ReadPort(int Length)
String Msg;
Msg = SB.GetMsg(Length);
return Msg;
* This function sends a message through the serial port.
* @param Msg The string to be sent.
public void WritePort(String Msg)
int c;
try
for (int i = 0; i < Msg.length(); i++)
out.write(Msg.charAt(i));
} catch (IOException e) {}
* This function closes the serial port in use.
public void ClosePort()
RT.stop();
serialPort.close();
----------------------------ReadSerial.java--------------------------------------
package serial;
import java.io.*;
* This class reads message from the specific serial port and save
* the message to the serial buffer.
public class ReadSerial extends Thread
private SerialBuffer ComBuffer;
private InputStream ComPort;
* Constructor
* @param SB The buffer to save the incoming messages.
* @param Port The InputStream from the specific serial port.
public ReadSerial(SerialBuffer SB, InputStream Port)
ComBuffer = SB;
ComPort = Port;
public void run()
int c;
try
while (true)
c = ComPort.read();
ComBuffer.PutChar(c);
} catch (IOException e) {}
------------------------------SerialBuffer.java-------------------------------------
package serial;
public class SerialBuffer
private String Content = "";
private String CurrentMsg, TempContent;
private boolean available = false;
private int LengthNeeded = 1;
* This function returns a string with a certain length from the incomin
* messages.
* @param Length The length of the string to be returned.
public synchronized String GetMsg(int Length)
LengthNeeded = Length;
notifyAll();
if (LengthNeeded > Content.length())
available = false;
while (available == false)
try
wait();
} catch (InterruptedException e) { }
CurrentMsg = Content.substring(0, LengthNeeded);
TempContent = Content.substring(LengthNeeded);
Content = TempContent;
LengthNeeded = 1;
notifyAll();
return CurrentMsg;
* This function stores a character captured from the serial port to the
* buffer area.
* @param t The char value of the character to be stored.
public synchronized void PutChar(int c)
Character d = new Character((char) c);
Content = Content.concat(d.toString());
if (LengthNeeded < Content.length())
available = true;
notifyAll();
Help me !!!

Answer 1

First thing to say is that you really should check if the initialisation was successful in
button1_actionPerformed()You should be checking the return value on the SerialBean Initialize() method. If the initialisation has failed, then the null pointer exception will be thrown because there will be no stream to write to.
I would also recommend rewriting the catches in the SerialBean Initialize() method to dump the stack trace from the caught exception and any additional information that the exception holds for example:
} catch (PortInUseException e) {
    e.printStackTrace();
    return InitFail;
}This will give you a lot more information to work with if it is an initialisation problem.